Refractory concrete and method of making



Patented Jan. 9, 1951 1 V UNITED S'i TENT QFF'ICE Roy T. Giles, DaytonaBeach, Fla.

No Drawing. Application September 9,1947, Serial No. 773,077

This invention relates to an improved refractory, more particularly arefractory concrete of which an essential component is calcium aluminatecement.

Among the objects of the invention is the provision of an improvedrefractory composition yielding articles such as refractory structuresand shapes of improved strength at elevated temperatures, and therefractory shapes resulting from such composition.

The present invention relates to the same general type of refractoryconcrete which is disclosed and claimed in Kocher Patent N 0. 2,416,700.The refractory concrete of the present invention contains as essentialcomponents calcium aluminate cement and a refractory material, eitherthe refractory material or the caTcium aluminate cement containing atleast 1% by weight of hydrogen fluoride, herein designated by itssymbol, HF. Preferably, when the HF is contained in the refractorymaterial such material is a granulated or comminuted calcined refractorymaterial initially containing, before calcination, a substantialquantity of combined water, and after calcination being composed to amajor degree of alumie ha, and containing from 1 to as high as about 25%by weight of hydrofluoric acid adsorbedor occluded therein, suchmaterial being referred to hereinafter as HF containing calcinedaluminous material. It is possible, however, to incorporate the HP infire clay grog, which maybe employed both as the HF bearing component ofthe mix and as the refractory aggregate therein.

It is also possible to incorporate the HP in the calcium aluminatecement itself. Thus the mix for forming the. refractory concrete of theinvention may consist essentially of a two component system, calciumaluminate cement and refractory material, either one of which bears therequisite amount of HF, or a three component system, calcium aluminatecement, refractory material bearing the requisite amount of HF, andrefractory aggregate or filler. The refractory concrete of the presentinvention, which may be employed for the same applications as thoseoutlined in the above Kocher patent, is made from a mix, theconstituents of which, in the case of the twocomponent system, liewithin the following limits given in per cent by weight of the totalweight of the mix:

Per cent Calcium aluminate cement s 5-60 Refractory material 95-40either one of such components containing at least ;l% byweight of HF. 1

6 Claims. (01. 106-64) In' the three-component system referred to abovethe mix lies within the following limitsv given in per cent by weight ofthe total weight of the mix:

Per cent Calcium aluminate cement 5-60 Refractory filler 0-945containing calcined aluminous material .5-95

The calcium aluminate cement employed is one which is known in theUnited States as Lumnite cement. Such cement is also referred to as highalumina, alumina, or fused cement. I

Considering the embodiment of the invention first above given, by HFcontaining calcined alumineus material as used in the specification andclaims, is meant a calcined material composed in at least its majorportion of A1203 and which contains, by being adsorbed or occludedthere-in, HF from a. minimum of 1% by weight to the maximum which it ispossible for such aluminous material to adsorb or occlude. Within suchterm is included calcined high-alumina cays containing HF as above, andcomposed of atleast by weight A1203 and having had initialiypresent,before calcination, a substantial quantity of combined water. Thecalcination is carried out at such a temperature and for such a timethat substantially all the combined Water is driven off from thealuminous material. Included in such group are the following materials,in which the partial analyses before and after calcination are given inper cent by weight:

Before Galcination After Oal-;. clnation, A1203 bined A120? First gradediaspora, Mo. 72. 4 l3. 5 84. 5 Dutch Guiana gibbsite- 5s. 4 30. 6 184.0Pure bauxite 73. 9 26. l Bauxite, Ga 54.0 16.1 64.5 Second gradediaspore, Mo 53. 3 12.0 59. 5

ous liquids and gases, so that they are widely used for purifyingvarious liquids and gases. Such adsorbing or occluding property of theabove given calcined aluminous materials appears to depend upon asurface condition of the materials, probably produced by driving off thecombined water therefrom, whereby a large surface receptive to theretention of liquids and gases is obtained in such materials. Animportant source of the HF containing calcined aluminous materialemployed as a constituent of the mix of this invention is the spentmaterial which has been employed for removing HF in the process of HFalkylation of isoparaffins and olefins with anhydrous hydrofluoric acidas a catalyst. Such process, which is described in an article entitledHF Alkylation on page 153 of the Oil and Gas Journal, March 30, 1946,requires that HF be removed from the bottoms obtained from theprefractionator. The calcined bauxite or activated alumina used for suchpurpose removes the last HF, which is normally combined with organicgroups, from such bottoms, such removal apparently involving a processof adsorption or occlusion of HF by such materials. Such adsorption ishighly preferential, so that only a small percentage of the organicmaterial is adsorbed or occluded. Activated alumina has the property ofbeing able to adsorb about 25% by weight of HF, whereas a calcinedhigh-alumina clay such as calcined bauxite adsorbs about by weight HF.When substantially complete saturation of such materials by HF occurs inthe alkylation process, such materials are discarded, being thendescribed as spent. Whereas such materials, containing approximately themaximum possible amount of HF adsorbed or occluded therein, areordinarily employed as addition agents in the concrete mixes of thepresent invention, such materials containing HF between the limits 1% byweight and the above maximum adsorptivity of each may be used inpracticing the invention.

The spent HF containing calcined aluminous materials obtained from theabove referred to alkylation process have been given by Way of aspecific source of the HF containing calcined aluminous materialemployed as an additive in the refractory concrete mix of the presentinvention. It is to be understood, however, that although such source ispresently to be preferred, as it utilizes an otherwise waste material,the HF containing calcined aluminous material" may be produced in otherways, as by contacting the above recited calcined aluminous materialsdirectly with HF as a liquid or vapor to produce an HF content of from1% up to the maximum possible adsorptivity of the material, if desired.

The refractory filler which may be used in the concrete mix is usuallyin the form of a refractory aggregate which may be fire. clay grog,crushed firebrick, expanded shale, olivine, fused alumina, chrome,magnesite, vermiculite, diatomaceous earth, crushed red-brick and thelike, or combinations of these materials depending upon the use to whichthe refractory concrete is to be put.

The constituents of the mix are supplied thereto in either comminuted orgranular form to allow them to be uniformly distributed throughout themix and consequently the resulting concrete. Those constituents whichform the bond are preferably finely ground to facilitate their reaction.The calcium aluminate cement, for example, may be of such fineness thatpractially 4 all particles will pass through a mesh screen, and the HFcontaining calcined aluminous material may be ground to any particlesize. The refractory filler or aggregate may be of any desired particlesize or range of particle size consistent with substantial uniformity ofdistribution through the resulting concrete. The particle size of theaggregate naturally will be chosen with the minimum section of the shapeor structure to be made in View.

The mix may conveniently be made by mixing "the calcium aluminatecement, the HF containing calcined aluminous material, and therefractory filler, if used, in dry condition to a uniform color, therefractory aggregate being thoroughly wet down with water and then addedto the mixture of the calcium aluminate cement and HF containingcalcined aluminous material. Sufficient Water is added to the resultingmixtur to render it workable, the amount added depending upon the mannerin which the mix is to be subsequently handled in the formation of theconcrete shape or structure. Thus, if the concrete is to be cast into amold or form, particularly if the shape is intricate, the mix should beof puddling consistency. For simple shapes so cast, less water may beused, whereas if the mix is to be tamped or vibrated into place ormolded under pressure, still less Water may be used. It is obvious thatsuflicient water should be used in all cases to develop full thhydraulic strength of the cement and that an excess of water should beavoided. Besides the variation in modes of handling the mix aboveindicated, it is possible to deposit it in a mold or form or in anydesired location, as for instance, in the applying of patches toexisting structures, by charging the mix into a cement gun which pumpsor otherwise forces it out through a discharge orifice.

After the mixture has been shaped or molded in any one of the ways abovedescribed, it i dried and then heated. Usually for bodies of largesection, such as cast furnace walls, the practice follows approximatelythat employed in the drying and heating of newly constructed firebricklinings. The concrete may be air dried for a period of several days,after which the furnace is heated at temperatures which graduallyincrease up to operating temperature. I Small bodies and shapes, such ascast bricks, atiles, and slabs may be kept for a time, on the 'order oftwenty-four hours in a high humidityconstant temperature atmosphere,dried at a low temperature, on the order of 230 F., and then subjectedto a high temperature approximating that at which the shape will beused, for example, 2000 F.

Concrete resulting from mixes in accordance with the present invention,after having been dried and heated as above, possesses increasedstrength, improved load bearing characteristics at elevatedtemperatures, and greater abrasion resistance at elevated temperaturesthan similar concretes similarly treated, made in accordance with theprior art.

Such increased strength and load bearing qualities of the concrete ofthe present invention at room temperatures are shown by the results setout by the following Tables I and II giving the compressive strengths of2 inch cubes made of mixtures containing the indicated percentages byweight of calcium aluminate cement, HF containing calcined aluminousmaterial, and refractory aggregate. In the making of such 2 inch testcubes the mix was made of a puddling consistency and poured into '2 inchcube molds. After treatment in a moist cabinet the cubes were dried at230 F., fired for the indicated length of time at the indicatedtemperature, and were then allowed to cool. After cooling, each cube wassubjected specimens fired for four days at 1600 F., however, thecompressive strength is initially decreased and does not becomeapproximately equal to that of a similar mix containing no admixture 5until 9. 1% by weight of the mix of such bauxite to a compressivestrength test at room temperais added. From this point, however, thereis obture by subjecting it to gradually increasing prestained a markedincrease in compressive strength sure until a point of failure of thecube was 7 with such firing upon addition of larger amounts reached. ofsuch bauxite.

In Table I, below, the mixes employed contained 10 It will be seen fromtest No. 6 in Table I above calcium aluminate cement, spent I-IFcontaining that substantially the same beneficial results are calcinedbauxite, and crushed firebrick. The calobtained if the HF containingspent calcined cium aluminate cement in all tests was ground to bauxiteis washed rather than recalcined to reasizesuchthat 14.7% remained ona325mesh sieve. move the volatile organic material. In this in- The HFcontaining calcined aluminous materials stance, at least, removal ofsuch material apwere, in the tests set out in both tables, ground pearsto have been more complete than is obto pass an 80 mesh sieve. Thecrushed fire'brick, tained by recalcining, since the compressive whichranged in particle size from inch to dust, strength of specimens firedfor four days at 1600 had the following specific screen analysis: F. isnoticeably larger than the similar strength for those of the similar mixemployed in test 4 8 14 28 48 100 Thru No. 5 in which the bauxite wasrecalcined.

- The following Table II gives the results of come pressive strengthtests con-ducted on specimens Crushed firebrick. 12.3 16.0 19.2 14.011.7 10.8 16.0 composed of calcium aluminate cementy HF r tainingactivated alumina and crushed fire- Each of the values given for eachtest in the folbrick, fired for twenty-four hours at 1600 F. lowingTables I and II represents the average of tests on three similar 2 inchcubes. The figures Table II under each heading in the tables representthe per cent of such material in the total batch by 30 Calcium speutuwCompressive weight. Aluminatc tivated -538%}, fif g" T bl I Cementalumina Compressivcfitrength Per cent Per cent Percent Calcium CrushedSpent 4Days Firing at l 0- 0 7 81 aluminate Fire- Calcmed 2 17.1 17.165.8 8,423 Cement brick Bauxite 1600 r. 2o0n1-.

1 24 Hrs. Firing at 1600 F. P g l 157 708 The results set out in TableII demonstrate 19.6 75.4 5.0 "821 2, 971 40 that increased compressivestrengths are ob- 3:: tained when HF containing calcined aluminous 7- -83,271 ,783 material other than bauxite is employed in accordance withthe invention. In this instance, the activated alumina was obtained asthe The H contammg calclned bauxlte employed spent HF removing materialfrom the alkylation i t s 2 t0 inclusive in Table I was that process andtherefore contained in the neighbortained as the Spent catalyst removingagent in hood of 25% HF. Such material was neither rethe process Set outabove, and therecalcined nor ashed before incorporated fore contained inthe neighborhood of 15% by inthemi ofTab1eII Weight The calcined bauxiteemployed in Although the use of calcined aluminous matests 2 to 5,inclusive, was submitted to a step terial as the HF hearing agent in themix and of recalcining at 1000 F. to remove therefrom con rete em loyingcal ium alu ninate cement volatile material which otherwise wouldinterhas been Set t above by Way 0f pecifi fem With the set of thecement- Such Volatile amples, it is to be understood that the inventionmaterial, Which appeared to be a minor Percentis not limited thereto. Asindicated earlier, the age, is thought to be gasoline or a similarvolatile calcium aluminate itself may he The HF bearing organic materialoccurring in the bottoms in the agent in t mix, or, when fire clay grogis alkylation pI'OCeSS. The recalcination at a: temployed a thepreponderant part of the refractory perature of 1000 F. was high enoughto drive aggregate 11-, may b used as the agent bearing oil such organicmaterial but not high enough to t amount f HF aheady defined The HF maydrive off more than perhaps a Very Small P be incorporated in thecalcium aluminate cecentage o the HR The Spent HF Containing ment or thefire clay grog by subjecting such calcined bauXite p y in test 6 inTable I materials in a suitable HF resistant container to was treated inan alternative manner to remove. Contact t liquid or gaseou HR The t u hl le a c material Such bauxite Was 5 ture of the calcium aluminateparticles and those submitted o a Wash reatment, which conof the fireclay grog is such that HF within the sisted of immersing the bauxite inwater for limits of 1 to about 15% by weight may be thus twenty-fourhours after which it was dried at incorporated in such materials,apparently by 230 F. processes involving adsorption or occlusion.

As seen from Table I, the addition of rela- The reason why refractoryconcretes containtively small amounts of spent HF containing calingcalcium aluminate cement and refractory cined bauxite markedly increasedthe compresmaterial, either of such components containing sive strengthsof specimens fired for four days HF, in accordance with the presentinvention, at 2000 R, such increased strength continuing possessincreased hot and cold strength loadupon increase of such bauxitecontent. With bearing qualities and abrasion resistance as compared tosimilar concretes without such HF bearing material is not fullyunderstood. The theory which seems most fully to accord with the factsas now known is that the fluorine or HF released upon heating of the mixand consequently heating of the HF containing material reacts with theother components of the bond to promote the formation of mullite,3Al2O3- 23102 in fine crystalline form.

Regardless of the correctness of such theory, however, it is possible toemploy the teaching of the present invention with concretes in which theHF containing material is not present in the mix, the concrete beingsubjected to the volatile products released by such HF containingmaterial when heated to at least 1400 F. and preferably to at least1660" F. in proximity to the concrete similarly heated. The variousmethods by which concrete may be subjected to volatile products of topazhave been set out in the above identified Kocher patent, and suchmethods may be practiced here in the same manner with the exception,however, that the concrete is treated with the volatile products fromthe HF containing material rather than those of topaz. Thus, theinvention may be practiced especially with smaller shapes, such asbricks, slabs, and tiles, by heating such shapes in a mulfie furnacewith a quantity of HF containing refractory material, which may be amongothers the above defined calcined aluminous material, in a crucible,likewise placed in the mufiie furnace. With larger shapes, such asfurnace walls and the like, the furnace and other part may be heatedpreparatory to being placed in service and thereafter subjected to theaction of an atmosphere ofthe volatile products of the HF containingrefractory materials. Such improvement in strength in refractoryconcrete containing calcium aluininate cement and refractory aggregatewithin the limits noted may also be attained, after the concrete hasbeen in service, by the diffusion into it at elevated temperatures ofthe volatile products given off by HF containing refractory materialwhen heated to at least 1%00" F., such heating of the body and the HFcontaining refractory material adjacent thereto, as stated, preferably 8being carried out ,at temperatures of at least 1600 F.

Whereasparticular embodiments of the invention have been described abovefor purposes of illustration, it will be evident that numerousvariations of details are possible within the teaching of the invention.

I claim:

1. A mix for making refractory concrete consisting of from 5 to 60% ofcalcium-aluminate cement and from 40 to 95% calcined clay containingfrom to 99% alumina, one of said components containing from 1 to 25%hydrogen fluoride.

2. A mix for making refractory concrete consisting of from 5 to ofcalcium-aluminate cement, from .5 to calcined clay containing from 50 to99% alumina and the balance substantially all refractory aggregateselected from the group consisting of fire-clay grog, crushed brick,expanded shale, olivine, fused alumina, chrome, magnesite, vermiculiteand diatomaceous earth, one of said components cement, clay andaggregate, containing from 1 to 25% hydrogen fluoride.

3. A mix for making refractory concrete consisting of from 5 to 60% ofcalcium-aluminate cement and from 40 to 95% calcined bauxite containingfrom 1 to 25% hydrogen fluoride.

4. A mix for making refractory concrete consisting of from 5 to 60% ofcalcium-aluminate cement and from .5 to 95% calcined bauxite containingfrom 1 to 25% hydrogen fluoride.

5. Refractory concrete formed from a mix consisting of from 5 to 60% ofcalcium-aluminate cement and from 40 to 95% calcined clay con tainingfrom 50 to 99% alumina, one of said components containing from 1 to 25%hydrogen fluoride.

6. In a method of making refractory concrete, the steps includingshaping a mix of calciumaluminate cement and subjecting the shaped massto contact with the gases evolved on heating to 1400 F. calcined claycontaining from 50 to 99% alumina and from 1 to 25% hydrogen fluoride.

ROY T. GILES.

No references cited.

1. A MIX FOR MAKING REFRACTORY CONCRETE CONSISTING OF FROM 5 TO 60% OFCALCIUM-ALUMINATE CEMENT AND FROM 40 TO 95% CALCINED CLAY CONTAININGFROM 50 TO 99% ALUMINA, ONE OF SAID COMPONENTS CONTAINING FROM 1 TO 25%HYDROGEN FLUORIDE.